This document claims benefit of priority under 35 U.S.C. xc2xa7119 to Japanese Patent Application Nos. 2000-012297, 2000-230153, 2000-398225, and 2000-396638, respectively filed in the Japanese Patent Office, on Jan. 20, Jul. 31, Dec. 27, and Dec. 27, 2000, the entire contents of each of which are hereby incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image forming apparatus, such as a printer, copying machine, facsimile device, etc., provided with a paper turning-over section in the paper conveying path extended from the paper feeding section to the image forming section, and in particular, an image forming apparatus provided with an image forming section of the electrophotographic type or digital electrophotographic type capable of conveying recording paper with high speed, or an image forming apparatus having a function of paper binding.
The present invention further relates to an image forming apparatus having a function of accommodating the recording paper from the front tip end thereof in a temporary paper accommodating section, switching back the recording paper such that the rear tip end of the recording paper becomes the front tip end thereof, and conveying the recording paper thus switched back to the printer engine.
The present invention further relates to an image forming apparatus capable of sufficiently shortening the distance between the preceding recording paper and the recording paper just subsequent thereto, in particular, at the time of the both-surfaces printing, or otherwise capable of at least partially superposing the preceding recording paper and the just subsequent recording paper on each other in the temporary paper accommodating section.
The present invention further relates to a printer, copying machine, facsimile device set, and complex machine, all provided with the above-mentioned image forming apparatus.
2. Discussion of the Background
Regarding such the sorts of technology, the inventions described in the published specifications of Japanese Laid-open Patent Publication Nos. 5-289453 and 8-259045 are well known.
Among those Japanese Laid-open Patents, the former Laid-open Patent (5-289453) discloses the sheet feeding section of an image forming apparatus capable of shortening the positional distance between the recording papers having the image formed thereon by the image forming section by conveying the recording paper with an increased conveying speed during a constant time period. If the paper distance is intended to be shortened with the increased conveying speed, when the paper conveying path from the paper feeding section to the position where the conveying speed starts to be increased is long, all of the recording papers existing in the conveying path have to be conveyed with the same increased conveying speed. For this reason, the control of changing the paper conveying speed inevitably becomes large-scaled, and that results in the occurrence of troublesome matters to be solved, such as the increase of cost, the increase of noise, etc., on some occasions. In such a situation, the background-art technology has enabled to successively convey the recording paper fed with a constant conveying speed/paper distance in the past, with the necessary paper conveying speed and with the very shortened paper distance, without transiently accelerating the recording paper to be conveyed by use of the method of shortening the paper distance utilizing the switch-back path.
Furthermore, the published specification of Japanese Laid-open Patent Publication No. 8-259045 discloses a paper re-feeding apparatus in an image forming apparatus, that is, a both-surfaces copying apparatus capable of turning over the recording paper having the image formed on the one-side surface thereof and re-feeding the recording paper thus turned over, in which two sheets of paper can be conveyed at the same time on the switch-back path in the paper turning-over device. The same specification further discloses the registration operation at the time of sending out the recording paper.
However, according to the above background art, since the advancing and sending-out operations are performed with three rollers successively brought into contact with each other so as to equalize the conveying speeds before and behind the recording paper turning-over apparatus, the paper distance cannot be largely shortened. Furthermore, the position where the registration operation is performed is largely shifted from the image forming device. Therefore, the image position is probably shifted therefrom due to the conveyance error occurring during the time period of conveying the recording paper on the path. For this reason, the functional effect is limited only to skewing function compensating.
Otherwise, as the related technology, the sheet-state material (e.g. paper) turning-over apparatus and the image as disclosed in the published specification of Japanese Laid-open Patent Publication No. 8-20106 and the sheet turning-over apparatus as disclosed in the published specification of Japanese Laid-open Patent Publication No. 5-97305 are well known. However, in both of them, the driving roller provided on the switch-back path can be parted therefrom and the advancing and sending-out operations for the recording paper can be performed at the same time in the both-surfaces copying machine same as that of the background art as disclosed in the aforementioned Japanese Laid-open Patent Publication No. 8-259045.
Here, the image forming apparatus provided with a paper turning-over device on the paper conveying path extending from the paper feeding stage to the image forming apparatus as proposed by the present inventor, et al. is described hereinafter.
FIG. 12 illustrates an example of an electrophotographic-type image forming device and an image forming apparatus provided with a paper turning-over device. In FIG. 12, the recording papers piled and accommodated in a paper feeding device 1 are separated and fed sheet by sheet from the uppermost position thereof. The recording paper thus separated and fed advances to the switch-back path by the action of the first conveying device 11 and the third conveying device 13 constructing the switch-back path. After stopping temporarily, the third conveying device 13 and the second conveying device 12 practice the registration operation. Thereafter, the recording paper is fed to the image forming device 2. After forming and fixing the image on the recording paper, the recording paper having the image formed thereon is discharged to the paper discharging device 6.
FIGS. 13 through 15 illustrate the registration operation at the time of forming the image on the recording paper in the image forming apparatus as shown in FIG. 12. As is apparent from the illustration of FIGS. 13-15, the leading tip end of the recording paper sent out from the switch-back path is detected by a registration sensor 15, and the sending-out operation of the third conveying device 13 is continued until a predetermined time period elapses. Thereafter, the operation of the third conveying device 13 is stopped. In such a state, the leading tip end of the recording paper impinges on the second conveying device 12 in a state of a little bending as shown in FIG. 14. By creating such a state, the leading tip end of the recording paper is caused to go forward along the nip portion of the second conveying device 12, and in such a state, the improvement of the accuracy in the skew compensation and the paper sending-out timing can be realized. The above operation is called xe2x80x9ca registration operationxe2x80x9d.
Here, among the advancing path for the recording paper and the other path of sending out the recording paper, the commonly-used paper conveying path is called xe2x80x9ca switch-back path 13axe2x80x9d, and the position where the recording paper is stopped by the switch-back device is called xe2x80x9ca turning-over stop positionxe2x80x9d (B position described later). During the time period of practicing the registration operation, the third conveying device 13 has to be stopped. If the conveying device 13 is not stopped, the just subsequent recording paper cannot be conveyed to the turning-over stop position B. In particular, the problem may become very serious when the stopping state continues for a long time, due to the paper feeding (conveying) timing compensation performed subsequently to the registration operation. Here, in order to solve or eliminate such a problem, the apparatus is constructed such that the second conveying device 12 is stopped again for compensating the paper conveying timing after the rear tip end Pr of the recording paper is parted from the third conveying device 13, as shown in FIG. 15. Thereby, since the just subsequent recording paper can be stopped after finishing the conveyance of the paper to the turning-over stop position B, the image formation can be done with an optional timing. Therefore, it may be preferable to largely shorten the distance between the recording papers and successively form the image. If the rear tip end of the recording paper cannot be parted from the third conveying device 13, sheltering devices 13b and 13c are provided in order not to obstruct the leading tip end Pf of the advancing recording paper.
FIGS. 18 and 19 are conveyance diagrams for illustrating the state of conveying the recording paper including the aforementioned switch-back operation. As shown in FIG. 18, the paper to be fed is conveyed to the turning-over stop position B with the conveying speed Va, and thereafter the paper is stopped temporarily. The time period of stopping the recording paper is previously set with a margin capable of absorbing the unevenness of the recording paper arrival time caused by slip occurring on the conveying roller of the paper feeding device, the slow-down of the conveying speed due to the time-elapsing frictional wearing, and the unevenness of the paper piling position. The unevenness of the recording paper arrival time is shown by a dot-and-dash line. Regarding such unevenness, in the image forming apparatus of the FRR type in which the lower-side roller of a pair of up-and-down rollers as shown in the present example is driven with a constant torque in an opposite direction to that of the paper conveying and thereby the recording paper is separated by the action of the so-called wiping operation, the conveying force overcoming the paper load generated by the paper feeding device is required for the conveying roller and the registration roller. Such a paper load is apt to be generated due to slipping and/or friction. Furthermore, when the conveying speed is changed halfway in the paper feeding or the paper feeding is stopped temporarily, the state of the dynamic friction varies. As a result, the unevenness is enlarged or the roller mark due to the roller friction or the roller rubbing (wearing-out) occurs on some occasions. It is necessary to pay attention to the above-mentioned problem. Since the paper turning-over device is provided in the present structure, there arises a merit that such a problem does not occur at all, compared with the case that the apparatus not provided with the paper turning-over device temporarily stops the paper feeding by use of the paper feeding device at the time of operating the registration.
Furthermore, in the case of feeding the paper successively, since the paper-feed stopping time is provided so as to previously absorb the unevenness on the turning-over stopping position, it is not necessary to prepare the comparatively long stopping time for absorbing the unevenness in the state of fitting to the registration operation. Consequently, it may be very advantageous in the fact that the positional distance between the recording papers is largely extended due to the unevenness absorption.
Furthermore, in the background-art structure, the conveying speed for the recording paper 2 after the registration operation is increased for the purpose of shortening the paper distance, and thereby the paper distance can be shortened. However, when the paper conveying speed is increased, it is necessary to construct the apparatus such that the speed of all the registration roller, the conveying roller, and the paper-feeding device can be increased. Therefore, it is not necessary to solve the newly-arizen problem. That is a very advantageous structure in those points mentioned heretofore.
Furthermore, in the electrophotographic system, since a charger, a writing device, a developing unit, a transferring unit, and a cleaning unit are arranged around the surface of the photosensitive drum, and the respective processes are practiced successively, the operation of temporarily stopping the photosensitive body by a paper distance cannot be performed. Regarding the life span of the image forming device represented by the photosensitive body, the photosensitive body idly rotates wastefully by the loss of the paper distance. Therefore, the photosensitive body may have to be replaced more often, and that results in an increase in maintenance costs.
Furthermore, in the digital electrophotographic system, the writing device of the laser beam scanner system is generally used. However, if the rotation number of the polygon motor exceeds 30,000 r.p.m., an expensive air bearing technology is required. The similar high-cost technology of scanning the plural laser beam at the same time is required, in order to avoid such problems as mentioned above. Therefore, it has been difficult to improve the image forming speed according to the general technology. Furthermore, owing to the level-up of the requirement of the image quality in the recent years, the improvement of the resolution is advancing year by year. However, it is necessary to largely increase the rotation number of the polygon motor. That is a large subject matter to be solved, for realizing the image forming apparatus of high image quality and high speed.
FIG. 19 is a conveying diagram for illustrating the state of performing the stopping operation, in which, after operating the registration, when a comparatively long stopping time period occurs for the timing compensation, the just subsequent recording paper(s) can be conveyed to the turning-over stopping position and the paper conveying is stopped also for timing compensation.
As to the additional background arts, the published specifications of Japanese Laid-open Patent Publications Nos. 9-12198, 8-259045, 8-20106, and 5-97305 disclose technologies, in which, after forming the image on one surface of the recording paper by use of the printer engine, the recording paper is guided to a switching back path and switched back on the path and the recording paper thus switched back is returned to the printer engine, and an image can be formed on the rear surface of the recording paper in such a way.
However, according to the technologies as disclosed in the above background-art documents, the switching-back image formation of the piled recording paper in the cassette or the tray cannot be attained. To state concretely, according to the above technologies, after performing the image formation on the one surface of the recording paper with the printer engine, the recording paper is switched back. in order to turn over the recording paper and return it again to the printer engine. However, in all of the above-mentioned background arts, when the recording papers piled and accommodated in the paper stock section such as a paper feeding cassette or tray are directly conveyed to the printer engine, the recording paper cannot be switched back and supplied to the printer engine.
Heretofore, the background arts regarding the image forming apparatus of the electrophotographic type have been described. However, according to such background arts, for instance the arts disclosed in the background-arts documents, e.g., the published specifications of Japanese Laid-open Patent Publication Nos. 5-289453, 8-259045, 8-20106, and 5-97305 and other relevant documents relating to the other image forming apparatus, there exists no advantageous functional effect for improving the above-mentioned image forming apparatus.
The present invention has been made in view of the above-discussed and other problems to address the above-mentioned defects and troublesome matters of the background arts. To state in more detail, a primary object of the present invention is to provide a novel image forming apparatus for improving the defects and troublesome matters of the background arts.
Namely, including the aforementioned well-known examples, in the image forming apparatus for separating and feeding the recording paper by use of the paper feeding device and performing the registration operation of matching the recording paper onto the image position just before the image forming device, the image formation is generally performed on the recording paper with the paper distance of at least several tens mm with the factors such as the unevenness of the recording paper tip end position at the time of separating the recording paper, the time-elapsing and environmental variation of the recording paper conveying speed, and the stopping time period for performing the registration. It has not previously been possible to shorten the above-mentioned paper. Furthermore, in order to shorten the paper distance, although it can be thought that the photosensitive body is stopped in the position corresponding to the area between the recording papers, it may be impossible in practice to perform the control operation in such a way.
Consequently, the distance between the recording papers to have an image formed thereon, that is, the so-called paper distance, requires the aforementioned paper distance of at least several tens mm. The largeness of the distance between the recording papers exerts an influence upon the efficiency of the image formation.
The present invention was made in consideration of such technical background. Thus, one object of the invention is to maintain the small size and low cost and to enable practicing the both-surfaces image formation with the same paper distance.
The present invention further intends to realize a novel image forming apparatus capable of accommodating the recording paper from the front tip end thereof in a temporary paper accommodating section, switching back the recording paper such that the rear tip end of the recording paper becomes the front tip end thereof, and conveying the recording paper thus switched back to the printer engine. The present invention further realizes a printer, a copying machine, a facsimile device set, and a complex machine, all having the above image forming apparatus.
In such an image forming apparatus, when the recording paper piled and accommodated in the paper stock section such as a paper feeding cassette or tray is directly conveyed to the printer engine, various sorts of further effective processings can be performed by switching back the recording paper, compared with the case of feeding the recording paper directly to the printer engine without performing such switching-back. The present inventor has already found the above fact.
The present invention aims at performing various sorts of effective operations and treatment to the recording paper for the purpose of image formation, compensating the traverse registration of the recording paper with a simple compensation device, and further compensating precisely the traverse registration thereof.
The present invention further aims at improving the visible appearance of a stamp shadow and enabling to easily supply ink to the stamping device at the time of stamping the recording paper.
The present invention still further aims at reducing the number of parts, enhancing the effect of the paper processing treatment, performing effective curling compensation and effective heating and cooling for the recording paper, and thereby realizing a small-sized apparatus, improvement in reliability, and low cost.
The present invention still further aims at easily realizing temperature adjustment.
The present invention still further aims at reducing the number of parts, improving image quality by sufficiently removing dirt or dust such as paper powder, improving the flatness or smoothness and the brilliance of the recording paper by sufficiently pressing the surface thereof, and uniformly and sufficiently performing coating with a coating agent, and thereby realizing a small-sized apparatus, improvement in reliability, and low-cost.
The present invention still further aims at reducing manufacturing cost by realizing a small-sized apparatus and parts number reduction for an image forming apparatus capable of printing an image on both surfaces of the recording paper.
The present invention still further aims at enabling the positions of the images formed on the both (front and rear) surfaces of the recording paper to stably coincide with each other, for the both-surfaces printing image forming apparatus. The present invention still further aims at realizing a novel image forming apparatus for performing image formation with an ordinary electrophotographic method and digital electrophotographic method, both capable of attaining the above-mentioned respective objects of the present invention.
The present invention still further aims at realizing a printer, copying machine, facsimile device set, and complex machine, all capable of attaining the above-mentioned respective objects of the present invention.
In the aforementioned background art, assuming that, only after the preceding recording paper is switched back in the paper switch-back path and sent out to the photosensitive body, the just subsequent recording paper is sent to the switch-back path, the distance between the preceding paper and the just subsequent paper cannot be sufficiently shortened. As a result, the high-speed successive paper feeding cannot be realized.
In order to solve such the troublesome matter, the present invention still further aims at providing a novel image forming apparatus capable of sufficiently shortening the distance between the preceding recording paper and the just subsequent recording paper and thereby realizing high-speed successive paper feeding. In particular, the invention aims at sufficiently shortening the distance therebetween at the time of performing the both-surfaces printing in order to realize high-speed successive paper feeding. Furthermore, the present invention aims at providing an apparatus which does not require a special device for prescribing the movement path for the preceding paper and the just subsequent paper intersecting therewith. Thereby, it is possible to simplify and keep a small-size apparatus, and the cost of manufacturing the apparatus can be largely reduced.